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What size Optimate Solar Charger do I need?

Posted by in Solar Lights and Chargers on May 08, 2019 . .

An Optimate solar charger is the best way to keep your car, vehicle or leisure battery charged when not in use so that it's ready for duty when you need it.

Keeping your battery charged with an Optimate solar charger has the following advantages:

  • Never be dissapointed by a flat battery again!
  • Keeping your battery fully charged will extend battery life and save you the cost of premature replacement
  • Optimate solar chargers have a charge controller included
  • The charge controller will prevent battery overcharging, prevent battery discharge at night and increase charging efficiency
  • The Optimate charge controller also gives battery state of charge and charging status information courtesy of coloured LED indicator lights
  • Simple " plug and play" installation and operation
  • Optimate SAE connectors allow Optimate solar to be interchanged with Optimate mains chargers
  • Can be left permanently connected or connect and disconnect as required
  • Safely charge all 12V lead acid batteries including wet cell, AGM, AGM Spiral Cell and Gel battery types
  • All components fully weatherproof
  • Huge range of Optimate accessories to meet your particular installation requirements

So if you need to charge your battery in a remote location with no mains power - whether that's in your garden shed or at the top of a mountain - an Otpimate Solar Charger is going to be perfect for you!

Rule of thumb guide to solar panel size

As a rough guide go for a minimum of 10W of solar for every 100Ah of battery capacity. This ratio is sufficient to meet maintenance charging to protect from natural battery drain in mid winter in UK. The ideal solar panel position is externally mounted facing due South angled towards the sun at it's midday peak (high in summer, low in winter). If this cannot be achieved go up a size of solar charger (or two if a lot of shading/poor orientation). If there are drains on the battery (such as an alarm etc) go up a size or two depending on the size of the load e.g up a size for a car alarm system, maybe up two or three sizes for multiple loads/ larger loads such as a bilge pump on a boat.

If you are not sure what size solar charger you require the following table may help.

OptiMate Solar Charger Size Choice Guide

Solar Panel Position:    Ideal  OK Poor
Loads (e.g. alarm):    None Some None Some None Some
Motorcycle 5Ah - 30Ah 10W 10W 10W 10W 20W 20W
Lawn Mower 10Ah - 35Ah 10W 10W 10W 10W 20W 20W
Small Car 50Ah - 70Ah 10W 10W 10W 20W 20W 20W
Medium Car 70Ah - 90Ah 10W 10W 10W 20W 20W 40W
Large Car/4x4 80Ah - 100Ah 10W 20W 20W 40W 40W 40W
Tractor/Boat 100Ah - 130Ah 10W 20W 20W 40W 40W 40W
Lorry/Larger Boat 100Ah - 150Ah 20W 40W 40W 40W 60W 80W


Table Key:

Solar Panel Position Ideal: Solar Panel outside, facing due South angled towards midday sun (low winter, high summer)

Solar Panel Position OK: As "Ideal" above but solar panel behind glass (eg windscreen*) OR Solar panel is outside but not facing due South but still facing somehwere South of due West or South of due East with solar panel angled towards sun at highest point possible.

Solar Panel Position Poor: Solar panel South of due West or due East as described in "OK" above but behind glass (e.g windscreen*) OR Solar panel outside facing somehwere North of due East or North of due West.

Loads None: No loads drawing from battery when battery is at rest

Loads Some: Low level loads may be drawing from battery when at rest (e.g. alarm)

For higher loads such as bilge pumps go as large as you can afford / physical size allows or contact us for more accurate advice specific to your requirements.

Above battery sizes are approximate based on typical battery capacity according to vehicle type. Please check actual battery capacity in Ah of your battery.

Please note that some vehicles may have 6V (eg some motorcycles) or 24V (eg many lorries) batteries. Optimate solar charger's can only be used to charge / maintain 12V batteries.

* Please note that installing behind tinted (rather than clear) glass can reduce solar panel output considerably and in this situation consideration should be given to installing a larger solar charger. 

If you have any questions or you're not sure please get in touch and we will be happy to advise on the  best solar charger for your specific situation.

12V Solar Charger

Last update: Jun 17, 2020
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